1. Field of the Invention
The invention is related to structures used for providing fault tolerance in computer data networks. Especially, the invention is related to such a network node as specified in the preamble of the independent claim directed to a network node.
2. Description of Related Art
Fault tolerance is an important feature in network nodes connecting networks to one another, such as a local area network of a company to the public Internet. Fault tolerance is typically achieved by arranging for other network nodes to take care of duties of a network node having a failure. This is typically realized by using more than one network node to take care of a certain task, dividing the load among the nodes, and arranging the load of a failed node to be divided among the working ones. Various ways for arranging the load of a failed node to be divided among the working nodes are known, For example, two RFC standards define such mechanisms for routers, namely RFC 2281 “Cisco Hot Standby Router Protocol” (HSRP) and RFC 2338 “Virtual Router Redundancy Protocol” (VRRP).
In the HSRP protocol a plurality of routers forming a HSRP group work in concert to present the illusion of a single virtual router to the hosts for which the routers provide service. One of these routers is known as the active router, and takes care of actual routing of the packets. If the active router fails, one of the other routers, i.e. one of the backup routers, assumes the packet forwarding duties of the active router. Each HSRP group has an IP address and a well known MAC address, which are used by hosts for transmission of data via the virtual router.
The VRRP protocol uses the concept of a virtual touter, whose address is used by hosts for transmitting datagrams. One of the routers running the VRRP protocol acts as the master for a virtual router, i.e. performs the duties of the virtual router. The VRRP protocol provides a mechanism for transferring the duties to another router in the case of failure of the master router. Each virtual router has an IP address and a MAC address, which are used by hosts for transmission of data via the virtual router.
Both of these protocols provide for redirection of IP traffic in case of device failures. However, they are complicated and generate some, signaling traffic overhead in the network for executing the protocol. If the local area network to which they are connected to is large, the actual routers running the protocols may be in different segments, which brings the additional problem of informing bridges joining different network segments that in which segment the device corresponding to the virtual MAC address currently resides.